Share screen on Teams is very easy.
First af all: start a meeting with someone, during this meeting you need to share your desktop or some application on your desktop.
To share click the “Share” Icon as I show in this image:
Now, on the bottom of the screen , Teams shows you all the windows you have opened on your desktop.
So you can choose what to share. If you want to share all your desktop selecet “Screen #1”, but if you want to share only one application, you have to select only that application.
It is very easy to share screen on Teams and it is very useful too.
This is official the procedure on Microsoft website